A. Field of Invention
This invention relates to DC-to-DC power supply converters, particularly those used in applications requiring multiple high voltage, low ripple outputs.
B. Description of Prior Art
In essence, a DC-to-DC converter is an apparatus designed to accept DC power at a first voltage and output DC power at a differing voltage. Typically, such devices operate by converting the DC input to AC, transforming the AC to a higher voltage and rectifying the higher level AC to provide the necessary DC output.
The power supply for a traveling wave tube (TWT) amplifier within an earth satellite presents special problems. Such a power supply must accept DC from a relatively low voltage power source (typically a solar array) and provide well-regulated, relatively ripple free high voltage power, in a simultaneous manner to a number of outputs having constantly varying loads.
The typical prior art DC-to-DC power converter for such an application accepts the DC source, chops it with a switching device, such as a transistor, reintegrates the signal with inductive and capacitive devices, converts the integrated DC signal to AC with a transistor inverter, transforms the AC to high voltage, rectifies the resultant to DC voltages and configures them to supply a number of outputs.
In such devices, the integration capacitance is physically located "downstream" from the chopper, between the copper inductor and the inverter. In the absence of such capacitance, the desired integration would be lacking, but the input means to the inverter would, because of the presence of the inductor, constitute a current source. The latter configuration would, therefore, limit the current drawn through the chopper and inverter transistors, even during non-steady-state conditions.
With the integration capacitance located as it is in the prior apparatus, the input means becomes a voltage source, because of the electrical energy stored in the intervening capacitor.
Accordingly, during start-up of such a converter, a large current is drawn through the chopper power switch and the inverter transistors, which can easily cause one or more to fail, unless they are highly over rated. Arcing, which can occur in TWT amplifiers, despite emphatic statements to the contrary by their manufacturers, can likewise cause current surges through all the power supply switching (chopper and inverter). Finally, because of unpredictable load variations in the TWT depressed collectors, and other factors, such conventional power supplies cannot satisfy the stringent ripple requirements imposed on TWT amplifiers in certain satellite communication system applications.